🌐EnglishEnglishDeutschEspañolItalianoPortuguêsSvenskaРусский中文日本語EntityQ4515035· pop 8· linked from 32 articlesHilbert's fourth problemone of twenty-three, asking to construct all metric spaces where lines resemble those on a sphereAvailable in 8 languagesEspañol中文РусскийPortuguêsGreekSvenskaUkrainianvia Wikidata sitelinks · CC0ConnectionsAmerican Mathematical SocietyEntitymathematicsEntityCategoriesFoundations of geometryGeometry problemsHilbert's problems